It has been known that while genes of similar function exist within and between widely diverse organisms, the DNA sequences may differ considerably. Indeed, the homology in protein products may be much greater than the homology in DNA sequences due to the degeneracy of the genetic code. Furthermore, related sequences also exist that may or may not have a gene function. Since cloning of related genes within and between species is usually based on complementation of function, it has been difficult to identify, chromosomally locate and clone related genes and sequences between organisms due to the lack of DNA homology.
Recently, Rayssiguier et al, 1989, Nature,342:842, demonstrated that in vivo recombination can be made to occur between divergent DNAs using appropriate mismatch repair mutants. However, Rayssiguier et al's methodology is limited and directed to an in vivo bimolecular system that occurs randomly between chromosomal molecules via recombination and is not designed for an in vitro scheme and does not provide a means for selection of related sequences from many different sources.